Complement activation promotes all of the following except:

Question

a. Cell lysis

b. Inflammation

c. Opsonization

d. Interferon release

e. Chemotaxis of neutrophils and other cell

Accepted Answer

Welcome back everyone. Here's your next question. Which of the following statements explains the mechanism of complement activation. A it involves the direct binding of antibodies to antigens on pathogens leading to the activation of complement proteins. B it occurs when pathogen associated molecular patterns. P A MP S are recognized by the pattern recognition receptors. Pr RS on immune cells triggering a cascade of complement protein activation. Choice C it is initiated by the release of interferons in response to viral infections which subsequently activate the complement system or choice D it is a result of the release of histamine from mast cells leading to the activation of complement proteins. So let's think about complement activation and what it is. And it does involve this cascade, an activation cascade of complement proteins which we see that is um common to all of our answers. I forgot to emphasize that in choice C. So all of our answers recognize that we have this activation of the complement proteins as a result of some event. So we need to correctly identify that. And our correct answer here is Choice B, it occurs when these pattern recognition receptors on the immune cells the PR RS recognize a pathogen associated molecular pattern P A MP. And this can happen in two different ways. So there's two pathways and they're called the classical and the alternative. So the classical pathway is when you have antibodies that bind two antigens, and then this antibody antigen complex is recognized by the Pr Rs those receptors. So you have the binding of antibodies antigens and then that complex is what's recognized and then that triggers the activation of the complement proteins. And the alternative pathway you have direct recognition of P A MP S on pathogen cells by the Pr Rs those packet pattern recognition receptors such as complement receptor three or CR three or the manos receptor. Mr those are examples of some of those receptors and that direct recognition by the Pr Rs leads to the activation of complement proteins. So both of these pathways little arrow from two pathways lead to the activation of this cascade of events lead to the activation of the complement proteins. So choice B correctly describes that again, there's two different types of things that are recognized, either this antibody antigen complex or direct recognition of P A MP S. And with this in mind, we can see why choice A is incorrect. A says it involves the direct binding of antibodies to antigens leading to the activation of complement proteins. So this is connected and sort of partially correct in that that binding of antibodies to antigens is related to this activation. But the particular mechanism by which it happens is that the complex itself, that antibody anti antigen complex is what's recognized by the Pr Rs. And it's that recognition that leads to the activation. So that one's a little bit tricky. But that's why choice A isn't correct. Again. When you look at, then choice B, that's clearly a better answer. So you might sort of start by picking choice A and then rule that out. When you see that choice B is a more full and correct explanation. Choice. He says it is initiated by the release of interferons in response to viral infections. But when that happens, uh interferons do not activate the complement system. Interferons help make uninfected cells resistant to a viral infection. So interferons do respond to viral infections but they don't activate the complement system. They activate signaling pathways in neighboring cells that are not infected yet to help make them resistant. So that's why choice choice C isn't correct. And then choice D it is a result of release of histamine from mast cells. Um that does not activate the complement system that is part of an allergic reaction. So wrong cause not what we're looking for. So choice D is not correct. And our answer here to which statement explains the mechanism of complement complement activation is choice B, it occurs when pathogen associated molecular patterns are recognized by pattern recognition receptors on immune cells, triggering A cascade of complement protein activation. See you in the next video.

Complement activation promotes all of the following except:
a. Cell lysis
b. Inflammation
c. Opsonization
d. Interferon release
e. Chemotaxis of neutrophils and other cell

Key Concepts

Complement System and Its Functions

Opsonization

Interferon Release

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